Which Selleys construction sealant do you need, and how do you choose?

Selleys construction silicone provides a durable, flexible seal for heavy-duty construction projects — bonding and sealing in tough environments where lasting strength and performance are required. In practice this is the section you want when the joint is structural or masonry rather than domestic: a brick or concrete movement joint, a perimeter seal, a penetration through a wall.

Five products sit here, and they separate on two questions. First, is the joint going to move a lot? Three of the five are described specifically for high movement. Second, is this a fire-rated application? One product in the section is, and it should not be substituted for by any of the others.

What this category covers

The product listing on the live category page is loaded dynamically and could not be captured, so this page is built from the five products the live sitemap lists under this path. It covers masonry sealing, high-movement joint sealing, fire-related sealing around pipes, and two polyurethane trade joint sealants.

How to choose

If you are sealing brick or concrete

Selleys Brick & Concrete Silicone is the product named for the substrate. It is described as suiting high-movement areas and providing a water-tight seal.

Masonry is where movement capability earns its keep. Brick and concrete expand and contract measurably with temperature, and a control or movement joint exists precisely so that movement has somewhere to go. A sealant that cannot accommodate it either splits down the middle or pulls away from one face — and the second failure is worse, because the joint looks intact while water runs behind it.

If the joint moves a lot but is not masonry

Selleys Pro Series Flexiseal Multipurpose Sealant is described as a strong, durable seal for high-movement areas, giving a water-tight seal that lasts. It is the general high-movement option in this section.

If you are specifying a polyurethane joint sealant

Two Pro Trade products cover the trade polyurethane requirement, and they are chosen against opposite priorities:

• Pro Trade Joint Sealant LM — a non-slumping polyurethane joint sealant with high movement capability, low modulus and excellent adhesive properties.
• Pro Trade Joint Sealant FC — a fast curing polyurethane adhesive and sealant with high flexibility and excellent adhesion.

Low modulus is the property to understand if you are choosing between them. A low-modulus sealant develops less stress as it is stretched, so it puts less load back into the substrate at the bond line. On a weak or friable substrate that is what keeps the sealant from tearing the surface away with it. Non-slumping means the bead holds its shape in a vertical or overhead joint rather than sagging before it cures.

Choose LM where movement and substrate protection dominate, and FC where the schedule does.

If the application is fire-rated

Selleys FlameFlex is described for sealing around pipes and other fire-rated applications, forming a fire-resistant barrier. It is the only product in this section described that way, and none of the others should be used in its place.

For the dedicated fire and acoustic range, including the products developed for perimeter and penetration seals in fire-rated construction, see fire rated sealants. Fire-rated work is selected against the construction specification rather than by general preference.

If you need bonding as well as sealing

Selleys 655FC Fast Cure Adhesive Sealant sits in the multi-purpose range and is described as a fast-curing, versatile product for bonding and sealing construction or automotive surfaces. Where the joint has to carry load as well as exclude water, compare it against the products above.

Where the job is purely bonding rather than sealing, the construction adhesives sit under glues and adhesives instead.

The products in this range

• Selleys Brick & Concrete Silicone — for brick and concrete surfaces, suits high-movement areas, gives a water-tight seal.
• Selleys Pro Series Flexiseal Multipurpose Sealant — strong, durable seal for high-movement areas.
• Selleys Pro Trade Joint Sealant LM — non-slumping polyurethane with high movement capability, low modulus and excellent adhesive properties.
• Selleys Pro Trade Joint Sealant FC — fast curing polyurethane adhesive and sealant with high flexibility and excellent adhesion.
• Selleys FlameFlex — for sealing around pipes and other fire-rated applications, forming a fire-resistant barrier.

The safety divide in this category — three of the five carry no classification at all

These five products look interchangeable on a shelf and are not. On hazard they fall into three groups, and the spread between the ends of it is as wide as anywhere in the Selleys sealant range.

Group	Products	Classification
Danger	FlameFlex	Reproductive toxicity — Category 1A, H360 (may damage fertility or the unborn child), plus eye irritation Category 2A
Warning	Brick & Concrete Silicone	H227 combustible liquid, H315 skin irritation, H317 may cause an allergic skin reaction
Not classified as hazardous	Pro Trade Joint Sealant LM, Pro Trade Joint Sealant FC, Flexiseal Multipurpose Sealant	No signal word, no hazard statements, and not Dangerous Goods by road, sea or air

The fire-rated product is the hazardous one, and the gap is not marginal. Category 1A is the most severe level of reproductive toxicity classification there is — a known or presumed human reproductive toxicant, not a suspected one. The practical consequence is blunt: anyone pregnant, who may become pregnant, or who is trying to conceive should not handle FlameFlex. On a job where fire-rated sealant is being installed in volume that belongs in the risk assessment, not left for an individual to work out from the cartridge. Nothing else in this category carries a health classification of that severity.

The three unclassified products are the genuinely useful finding. All three are polyurethane or hybrid construction sealants, and polyurethane is the family where you would most expect a sensitisation classification to appear — free isocyanate monomer is the usual cause. None of these three carries one. If the deciding factor is a confined space, a household with someone asthmatic, an occupied building, or simply not wanting to think about protective equipment, the two Pro Trade joint sealants and Flexiseal are the ones with nothing to declare.

Brick & Concrete Silicone sits in between, and its H317 is the one to act on. Sensitisation is permanent once acquired and is built up by repeated casual contact — exactly what a long run of masonry joints tooled bare-handed delivers. This is a sealant that invites it, with 35 minutes of tooling time and a 70-minute skin time. Wear gloves for the whole run, not just the first cartridge.

Comparing these sealants on the numbers that decide the joint

Movement capability decides whether the joint survives; modulus decides what the joint does to the substrate around it; service temperature decides where it can go at all. Flexiseal publishes no technical specification table, so it is left out of the comparison rather than estimated.

Product	Movement capability	Modulus at 100% elongation	Service temperature	Cure rate
Brick & Concrete Silicone	±50% (ISO 9047)	0.26 MPa	Approx. −40°C to 140°C	2mm per 24 hours
Pro Trade Joint Sealant LM	±25% (EN 15651)	0.35–0.40 N/mm²	−40°C to +90°C	2.5mm per 24 hours
Pro Trade Joint Sealant FC	±25%	0.35–0.40 N/mm²	−40°C to +70°C	Min. 3mm per 24 hours
FlameFlex	±20% (ISO 9047)	0.67 MPa	−40°C to 90°C	2–3mm per day

The product named LM is not the lowest-modulus sealant here. Low modulus is the property this page explains above — less stress fed back into the substrate as the joint stretches, which is what protects a weak or friable surface from being torn away by its own sealant. Pro Trade Joint Sealant LM publishes 0.35–0.40 N/mm² at 100% elongation. Brick & Concrete Silicone publishes 0.26 MPa, and carries the ISO 11600 Type F Class 25LM designation in its own right. On the published figures the masonry silicone is the softer, gentler sealant of the two, at double the movement capability. Where a low-modulus joint on old or friable masonry is the requirement, that is worth knowing before the trade badge decides it.

LM and FC publish identical movement capability, so the choice between them is not really about movement. Both are ±25%. What separates them on the numbers is elongation at break — 600% for LM against 400% for FC — and service temperature, where LM runs to +90°C and FC stops at +70°C. That 20 degrees is the one to watch on a dark-coloured facade, a plant deck or a roof-level joint in an Australian summer, where surface temperatures get well past air temperature. And "fast cure" describes depth, not surface: FC cures a minimum 3mm per 24 hours against LM's 2.5mm, but LM can be tack-free in as little as 20 minutes where FC takes 40 ± 10. If what you need is to get a joint closed and out of the weather quickly, the tack-free figure is the one that matters.

The fire-rated sealant is also the stiffest and the least tolerant of movement — ±20% and 0.67 MPa, the highest modulus in the category and less than half the movement capability of Brick & Concrete Silicone. That is not a criticism of the product; a fire-rated sealant is formulated to survive a fire, and the movement figure is what it costs. It does mean a penetration or perimeter joint that both moves seasonally and needs a fire rating is a design problem rather than a product choice, and it is settled against the construction specification and the fire rated sealants range, not by substituting a more flexible sealant in.

Common questions

Which sealant should I use on a brick or concrete joint?

Brick & Concrete Silicone is the product named for those substrates, and it is described as suiting high-movement areas.

What is the difference between Pro Trade Joint Sealant LM and FC?

LM is a non-slumping polyurethane with high movement capability and low modulus. FC is a fast curing polyurethane adhesive and sealant with high flexibility. Choose LM for movement, FC for speed.

What does low modulus mean in practice?

A low-modulus sealant develops less stress as the joint moves, so it transfers less load into the surfaces it is bonded to. That matters most on substrates that could be damaged by a stiffer sealant pulling on them.

What does non-slumping mean?

The bead holds its shape in a vertical or overhead joint instead of sagging before it cures, which is what makes a sealant usable on anything other than a flat horizontal joint.

Can I use any of these for a fire-rated seal?

FlameFlex is the one described for fire-rated applications and for forming a fire-resistant barrier. For fire and acoustic rated construction generally, use the dedicated fire rated sealants range and follow the specification.

Is a construction sealant suitable for a bathroom?

Nothing in this section is described for wet area use. Bathrooms, kitchens and laundries are covered by wet area silicone, which is formulated against mould and fungus growth.

Where do I find construction adhesives rather than sealants?

Under glues and adhesives. Sealants close joints; adhesives bond components, and the two are specified differently.